binutils-gdb/gdb/x86-nat.c
Maciej W. Rozycki 0d5ed15352 Avoid software breakpoint's instruction shadow inconsistency
This change:

commit b775012e84
Author: Luis Machado <luisgpm@br.ibm.com>
Date:   Fri Feb 24 15:10:59 2012 +0000

    2012-02-24  Luis Machado  <lgustavo@codesourcery.com>

	* remote.c (remote_supports_cond_breakpoints): New forward
	declaration.
[...]

changed the way breakpoints are inserted and removed such that
`insert_bp_location' can now be called with the breakpoint being handled
already in place, while previously the call was only ever made for
breakpoints that have not been put in place.  This in turn caused an
issue for software breakpoints and targets for which a breakpoint's
`placed_address' may not be the same as the original requested address.

The issue is `insert_bp_location' overwrites the previously adjusted
value in `placed_address' with the original address, that is only
replaced back with the correct adjusted address later on when
`gdbarch_breakpoint_from_pc' is called.  Meanwhile there's a window
where the value in `placed_address' does not correspond to data stored
in `shadow_contents', leading to incorrect instruction bytes being
supplied when `one_breakpoint_xfer_memory' is called to supply the
instruction overlaid by the breakpoint.

And this is exactly what happens on the MIPS target with software
breakpoints placed in microMIPS code.  In this case not only
`placed_address' is not the original address because of the ISA bit, but
`mips_breakpoint_from_pc' has to read the original instruction to
determine which one of the two software breakpoint instruction encodings
to choose as well.  The 16-bit encoding is used to replace 16-bit
instructions and similarly the 32-bit one is used with 32-bit
instructions, to satisfy branch delay slot size requirements.

The mismatch between `placed_address' and the address data in
`shadow_contents' has been obtained from leads to the wrong encoding
being used in some cases, which in the case of a 32-bit software
breakpoint instruction replacing a 16-bit instruction causes corruption
to the adjacent following instruction and leads the debug session astray
if execution reaches there e.g. with a jump.

To address this problem I made the change below, that adds a
`reqstd_address' field to `struct bp_target_info' and leaves
`placed_address' unchanged once it has been set.  This ensures data in
`shadow_contents' is always consistent with `placed_address'.

This approach also has this good side effect that all the places that
examine the breakpoint's address see a consistent value, either
`reqstd_address' or `placed_address', as required.  Currently some
places see either the original or the adjusted address in
`placed_address', depending on whether they have been called before
`gdbarch_remote_breakpoint_from_pc' or afterwards.  This is in
particular true for subsequent calls to
`gdbarch_remote_breakpoint_from_pc' itself, e.g. from
`one_breakpoint_xfer_memory'.  This is also important for places like
`find_single_step_breakpoint' where a breakpoint's address is compared
to the raw value of $pc.

	* breakpoint.h (bp_target_info): Add `reqstd_address' member,
	update comments.
	* breakpoint.c (one_breakpoint_xfer_memory): Use `reqstd_address'
	for the breakpoint's address.  Don't preinitialize `placed_size'.
	(insert_bp_location): Set `reqstd_address' rather than
	`placed_address'.
	(bp_target_info_copy_insertion_state): Also copy `placed_address'.
	(bkpt_insert_location): Use `reqstd_address' for the breakpoint's
	address.
	(bkpt_remove_location): Likewise.
	(deprecated_insert_raw_breakpoint): Likewise.
	(deprecated_remove_raw_breakpoint): Likewise.
	(find_single_step_breakpoint): Likewise.
	* mem-break.c (default_memory_insert_breakpoint): Use
	`reqstd_address' for the breakpoint's address.  Don't set
	`placed_address' or `placed_size' if breakpoint contents couldn't
	have been determined.
	* remote.c (remote_insert_breakpoint): Use `reqstd_address' for
	the breakpoint's address.
	(remote_insert_hw_breakpoint): Likewise.  Don't set
	`placed_address' or `placed_size' if breakpoint couldn't have been
	set.
	* aarch64-linux-nat.c (aarch64_linux_insert_hw_breakpoint): Use
	`reqstd_address' for the breakpoint's address.
	* arm-linux-nat.c (arm_linux_hw_breakpoint_initialize): Likewise.
	* ia64-tdep.c (ia64_memory_insert_breakpoint): Likewise.
	* m32r-tdep.c (m32r_memory_insert_breakpoint): Likewise.
	* microblaze-linux-tdep.c
	(microblaze_linux_memory_remove_breakpoint): Likewise.
	* monitor.c (monitor_insert_breakpoint): Likewise.
	* nto-procfs.c (procfs_insert_breakpoint): Likewise.
	(procfs_insert_hw_breakpoint): Likewise.
	* ppc-linux-nat.c (ppc_linux_insert_hw_breakpoint): Likewise.
	* ppc-linux-tdep.c (ppc_linux_memory_remove_breakpoint): Likewise.
	* remote-m32r-sdi.c (m32r_insert_breakpoint): Likewise.
	* remote-mips.c (mips_insert_breakpoint): Likewise.
	* x86-nat.c (x86_insert_hw_breakpoint): Likewise.
2014-10-03 12:54:34 +01:00

315 lines
9.3 KiB
C

/* Native-dependent code for x86 (i386 and x86-64).
Copyright (C) 2001-2014 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include "defs.h"
#include "x86-nat.h"
#include "gdbcmd.h"
#include "inferior.h"
/* Support for hardware watchpoints and breakpoints using the x86
debug registers.
This provides several functions for inserting and removing
hardware-assisted breakpoints and watchpoints, testing if one or
more of the watchpoints triggered and at what address, checking
whether a given region can be watched, etc.
The functions below implement debug registers sharing by reference
counts, and allow to watch regions up to 16 bytes long. */
/* Low-level function vector. */
struct x86_dr_low_type x86_dr_low;
/* Per-process data. We don't bind this to a per-inferior registry
because of targets like x86 GNU/Linux that need to keep track of
processes that aren't bound to any inferior (e.g., fork children,
checkpoints). */
struct x86_process_info
{
/* Linked list. */
struct x86_process_info *next;
/* The process identifier. */
pid_t pid;
/* Copy of x86 hardware debug registers. */
struct x86_debug_reg_state state;
};
static struct x86_process_info *x86_process_list = NULL;
/* Find process data for process PID. */
static struct x86_process_info *
x86_find_process_pid (pid_t pid)
{
struct x86_process_info *proc;
for (proc = x86_process_list; proc; proc = proc->next)
if (proc->pid == pid)
return proc;
return NULL;
}
/* Add process data for process PID. Returns newly allocated info
object. */
static struct x86_process_info *
x86_add_process (pid_t pid)
{
struct x86_process_info *proc;
proc = xcalloc (1, sizeof (*proc));
proc->pid = pid;
proc->next = x86_process_list;
x86_process_list = proc;
return proc;
}
/* Get data specific info for process PID, creating it if necessary.
Never returns NULL. */
static struct x86_process_info *
x86_process_info_get (pid_t pid)
{
struct x86_process_info *proc;
proc = x86_find_process_pid (pid);
if (proc == NULL)
proc = x86_add_process (pid);
return proc;
}
/* Get debug registers state for process PID. */
struct x86_debug_reg_state *
x86_debug_reg_state (pid_t pid)
{
return &x86_process_info_get (pid)->state;
}
/* See declaration in i386-nat.h. */
void
x86_forget_process (pid_t pid)
{
struct x86_process_info *proc, **proc_link;
proc = x86_process_list;
proc_link = &x86_process_list;
while (proc != NULL)
{
if (proc->pid == pid)
{
*proc_link = proc->next;
xfree (proc);
return;
}
proc_link = &proc->next;
proc = *proc_link;
}
}
/* Clear the reference counts and forget everything we knew about the
debug registers. */
void
x86_cleanup_dregs (void)
{
/* Starting from scratch has the same effect. */
x86_forget_process (ptid_get_pid (inferior_ptid));
}
/* Insert a watchpoint to watch a memory region which starts at
address ADDR and whose length is LEN bytes. Watch memory accesses
of the type TYPE. Return 0 on success, -1 on failure. */
static int
x86_insert_watchpoint (struct target_ops *self,
CORE_ADDR addr, int len, int type,
struct expression *cond)
{
struct x86_debug_reg_state *state
= x86_debug_reg_state (ptid_get_pid (inferior_ptid));
return x86_dr_insert_watchpoint (state, type, addr, len);
}
/* Remove a watchpoint that watched the memory region which starts at
address ADDR, whose length is LEN bytes, and for accesses of the
type TYPE. Return 0 on success, -1 on failure. */
static int
x86_remove_watchpoint (struct target_ops *self,
CORE_ADDR addr, int len, int type,
struct expression *cond)
{
struct x86_debug_reg_state *state
= x86_debug_reg_state (ptid_get_pid (inferior_ptid));
return x86_dr_remove_watchpoint (state, type, addr, len);
}
/* Return non-zero if we can watch a memory region that starts at
address ADDR and whose length is LEN bytes. */
static int
x86_region_ok_for_watchpoint (struct target_ops *self,
CORE_ADDR addr, int len)
{
struct x86_debug_reg_state *state
= x86_debug_reg_state (ptid_get_pid (inferior_ptid));
return x86_dr_region_ok_for_watchpoint (state, addr, len);
}
/* If the inferior has some break/watchpoint that triggered, set the
address associated with that break/watchpoint and return non-zero.
Otherwise, return zero. */
static int
x86_stopped_data_address (struct target_ops *ops, CORE_ADDR *addr_p)
{
struct x86_debug_reg_state *state
= x86_debug_reg_state (ptid_get_pid (inferior_ptid));
return x86_dr_stopped_data_address (state, addr_p);
}
/* Return non-zero if the inferior has some watchpoint that triggered.
Otherwise return zero. */
static int
x86_stopped_by_watchpoint (struct target_ops *ops)
{
struct x86_debug_reg_state *state
= x86_debug_reg_state (ptid_get_pid (inferior_ptid));
return x86_dr_stopped_by_watchpoint (state);
}
/* Insert a hardware-assisted breakpoint at BP_TGT->reqstd_address.
Return 0 on success, EBUSY on failure. */
static int
x86_insert_hw_breakpoint (struct target_ops *self, struct gdbarch *gdbarch,
struct bp_target_info *bp_tgt)
{
struct x86_debug_reg_state *state
= x86_debug_reg_state (ptid_get_pid (inferior_ptid));
bp_tgt->placed_address = bp_tgt->reqstd_address;
return x86_dr_insert_watchpoint (state, hw_execute,
bp_tgt->placed_address, 1) ? EBUSY : 0;
}
/* Remove a hardware-assisted breakpoint at BP_TGT->placed_address.
Return 0 on success, -1 on failure. */
static int
x86_remove_hw_breakpoint (struct target_ops *self, struct gdbarch *gdbarch,
struct bp_target_info *bp_tgt)
{
struct x86_debug_reg_state *state
= x86_debug_reg_state (ptid_get_pid (inferior_ptid));
return x86_dr_remove_watchpoint (state, hw_execute,
bp_tgt->placed_address, 1);
}
/* Returns the number of hardware watchpoints of type TYPE that we can
set. Value is positive if we can set CNT watchpoints, zero if
setting watchpoints of type TYPE is not supported, and negative if
CNT is more than the maximum number of watchpoints of type TYPE
that we can support. TYPE is one of bp_hardware_watchpoint,
bp_read_watchpoint, bp_write_watchpoint, or bp_hardware_breakpoint.
CNT is the number of such watchpoints used so far (including this
one). OTHERTYPE is non-zero if other types of watchpoints are
currently enabled.
We always return 1 here because we don't have enough information
about possible overlap of addresses that they want to watch. As an
extreme example, consider the case where all the watchpoints watch
the same address and the same region length: then we can handle a
virtually unlimited number of watchpoints, due to debug register
sharing implemented via reference counts in i386-nat.c. */
static int
x86_can_use_hw_breakpoint (struct target_ops *self,
int type, int cnt, int othertype)
{
return 1;
}
static void
add_show_debug_regs_command (void)
{
/* A maintenance command to enable printing the internal DRi mirror
variables. */
add_setshow_boolean_cmd ("show-debug-regs", class_maintenance,
&show_debug_regs, _("\
Set whether to show variables that mirror the x86 debug registers."), _("\
Show whether to show variables that mirror the x86 debug registers."), _("\
Use \"on\" to enable, \"off\" to disable.\n\
If enabled, the debug registers values are shown when GDB inserts\n\
or removes a hardware breakpoint or watchpoint, and when the inferior\n\
triggers a breakpoint or watchpoint."),
NULL,
NULL,
&maintenance_set_cmdlist,
&maintenance_show_cmdlist);
}
/* There are only two global functions left. */
void
x86_use_watchpoints (struct target_ops *t)
{
/* After a watchpoint trap, the PC points to the instruction after the
one that caused the trap. Therefore we don't need to step over it.
But we do need to reset the status register to avoid another trap. */
t->to_have_continuable_watchpoint = 1;
t->to_can_use_hw_breakpoint = x86_can_use_hw_breakpoint;
t->to_region_ok_for_hw_watchpoint = x86_region_ok_for_watchpoint;
t->to_stopped_by_watchpoint = x86_stopped_by_watchpoint;
t->to_stopped_data_address = x86_stopped_data_address;
t->to_insert_watchpoint = x86_insert_watchpoint;
t->to_remove_watchpoint = x86_remove_watchpoint;
t->to_insert_hw_breakpoint = x86_insert_hw_breakpoint;
t->to_remove_hw_breakpoint = x86_remove_hw_breakpoint;
}
void
x86_set_debug_register_length (int len)
{
/* This function should be called only once for each native target. */
gdb_assert (x86_dr_low.debug_register_length == 0);
gdb_assert (len == 4 || len == 8);
x86_dr_low.debug_register_length = len;
add_show_debug_regs_command ();
}